Abstract

The Carboneras fault system is a 40 km long, 1 km wide Neogene NE-SW-trending left-lateral transpressional strike-slip fault system which is part of the Trans-Alboran shear zone in SE Spain. The Carboneras fault system is an anastomosing array of sub-vertical, individual fault planes or fault zones which surround pods or lenses of less intensely strained rocks. Displacements along the individual fault planes exhibit reverse components of slips and form positive flower structures. Faults have either sharp boundaries or wider bands of gouge, typically a few metres thick and are hundreds of metres in length. Second-order fault splays are well developed and usually exhibit P-shear rather than Riedel-shear orientations. These are interpreted to be related to the transpressional displacement and may also characterize other oblique convergent zones elsewhere. The second-order faults are interpreted to have formed as shear strain increased along the first-order fault and was transferred laterally to branch segments. This process produced pods, or shear lenses, bounded by the fault segments. The length to width aspect ratios of the shear lenses were found to be scale-independent across five orders of magnitude with the most common values between 3:l and 6:l. A model is proposed for the development of the fault zone by incremental finite displacements along the segmented fault surfaces. This model is based on field evidence that displacement switched with time from one fault strand to another.